This invention relates to a solid-state laser device for use in emitting an output laser beam by pumping a solid-state laser medium by a semiconductor laser unit.
In a conventional solid-state laser device of the type described, a solid-state laser medium, such as Nd:YAG, is arranged in a laser resonator and pumped by an excitation laser beam to oscillate an output laser beam. Specifically, the solid-state laser medium has a pair of end surfaces and a side surface contiguous to the end surfaces and emits an oscillation laser beam along an optical axis extended through the end surfaces when the solid-state laser medium is excited by the excitation laser beam. The oscillation laser beam is generated as the output laser beam through the laser resonator. Herein, it is to be noted here that the excitation laser beam is usually generated by a semiconductor laser diode and is given to the solid-state laser medium and is irradiated onto either at least one of the end surfaces of the solid-state laser medium or the side surface of the solid-state laser medium.
In addition, it often happens that a wavelength conversion element, such as KTP, is located inside or outside of the laser resonator so as to emit the output laser beam which has a wavelength different from that of the oscillation laser beam. This structure enables oscillation of a blue or a green laser beam. Herein, such a wavelength conversion element will be generally called an optical function element.
At any rate, the solid-state laser medium and the wavelength conversion element are subjected to thermal control to stably oscillate the output laser beam. This means that the output laser beam should be invariable in intensity.
In the meantime, it is a recent trend that such a solid-state laser device is applicable to a wide variety of equipments and that a strict limitation is very often imposed on intensity of the output laser beam. In this connection, the intensity of the output laser beam should be always strictly stabilized for a whole duration of an operation of the solid-state laser device.
However, it has been found out that the above-mentioned thermal control can respond neither to a quick change of an atmospheric temperature nor to a temperature change which transiently occurs for a warm-up duration immediately after the operation is started in the solid-state laser device. In other words, such a quick change of the temperature brings not only about variations of characteristics of the solid-state laser medium and the optical function element but also about a relative relationship of positions between the solid-state laser medium and the optical function element. In addition, the quick change of the temperature results in a change of an oscillation condition of the laser resonator also. Thus, the intensity of the output laser beam inevitably fluctuates due to a vibration and/or aging of the solid-state laser device.